chore(auth): Move SignIn and ConfirmSignIn to use cases

[mattcreaser]

• PR title and description conform to Pull Request guidelines.

Issue #, if available:

Description of changes:

• Moves the SignIn and ConfirmSignIn functionality into coroutine-based usecases.
• Removes hasNewResponse flags from states because they are no longer necessary to work around threading issues.
• Further consolidates state handling logic between signIn, confirmSignIn, and autoSignIn.
• Increased unit test coverage of signIn and confirmSignIn

How did you test these changes?

• Additional unit tests
• Manual verification of various sign in flows

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Ensure commit message has the appropriate scope (e.g fix(storage): message, feat(auth): message, chore(all): message)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

❌ Patch coverage is 70.81712% with 75 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.52%. Comparing base (15c04fa) to head (d3e8ba2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3140      +/-   ##
==========================================
+ Coverage   54.34%   54.52%   +0.17%     
==========================================
  Files        1041     1044       +3     
  Lines       31360    31259     -101     
  Branches     4708     4695      -13     
==========================================
+ Hits        17043    17044       +1     
+ Misses      12479    12381      -98     
+ Partials     1838     1834       -4     

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